Liquid spill devices are usually required and installed as part of a closed liquid transfer system to prevent catastrophic tank failure by rupture in the event a tank is overfilled. A closed transfer system (also called a vapor recovery system) allows liquid cargo to flow from a sender facility, such as a terminal, to a receiving facility, such as a tanker vessel, and accommodates a flow of vapors or gases that occupy the tanks of the receiving facility back to the sending facility. Thus, no cargo in the form of gas or vapor is emitted to the atmosphere. While in theory the process for such liquid transfer appears simple, in practice a number of problems are encountered.
Among the many problems that must be dealt with in a closed liquid transfer system is the provision of some means of knowing and tracking liquid levels in various tanks to accommodate custody transfer and to prevent liquid overfill. Pressure in the tanks must be regulated or controlled to prevent tanks from being overpressured or underpressured, either of which could result in catastrophic tank failure. If tank pressure regulation or control fails, means must be provided to relieve the pressure or vacuum in the tank to prevent catastrophic failure. Furthermore, if the tank is overfilled, means must be provided to allow the liquid to spill out of the tank to prevent catastrophic tank failure. There are numerous methods of dealing with each of the above problems and, for instance, for inland and coastal navigational purposes, the U.S. Coast Guard has developed and implemented regulations for such systems in tanker or barge vessels. The most recent regulations are included in 46 CFR .sctn..sctn. 30 et seq.
SUMMARY OF THE INVENTION
This invention is directed to a liquid spill device arrangement for use in a closed liquid transfer system from a sender facility to a receiver vessel. The invention has particular application in transfer systems between a terminal shore facility and a tanker cargo vessel on an inland or coastal waterway. The spill device arrangement of this invention prevents catastrophic tank failure by rupture in the event a tank is overfilled. Also, the invention provides a spill device arrangement that works in conjunction with a backup system on the receiver vessel for control of gas/vapor of cargo liquids in the event of failure of the primary control system of the sending facility.
In a preferred form, the liquid spill device arrangement works in conjunction with a primary control system for pressurized transfer of liquid from a sender facility, such as an inland terminal, to a receiver vessel, such as a tanker vessel, and for transfer of gas/vapor from the receiver vessel to the sender facility. The receiver vessel has multiple tanks for containment of liquid with a common boundary between the tanks. A pressure relief means for venting gas/vapor at a selected relief pressure from the receiver vessel to atmosphere is provided when the pressure of the control system is exceeded. In one preferred form, a top of each tank has an opening therein in proximity to the common boundary. More broadly stated, the tanks have an opening near their tops in proximity to the common boundary. A closed trunk connects the tanks through the openings, or common opening, and allows liquid to flow from one tank to another. The liquid spill device is mounted in the trunk in communication with the tanks and opens at a pressure allowing overfill liquid to flow from containment in said tanks to prevent exceeding their structural design pressure. The liquid spill device opens at a pressure equal to or greater than the selected gas/vapor relief pressure of the receiver vessel.
These advantages and other objectives of this invention will be further understood with reference to the following drawings and detailed description.